The present invention relates to an organic electroluminescent (EL) device and a manufacturing method thereof; and, more particularly, to an organic EL device having a pair of electrodes at least one of which is transparent and a thin film made of an organic compound deposited between the electrodes, and a method for the manufacture thereof.
There is shown in FIG. 1 a schematic cross sectional view of a prior art organic electroluminescent (EL) device 31.
As shown, the organic EL device 31 comprises a substrate 32 made of, e.g., glass, an anode layer 34 formed on the substrate 32 and a cathode layer having a plurality of cathodes 35, and a thin-film organic layer 33 formed between the anode layer 34 and the cathode layer and incorporating therein a luminous layer made of an organic compound. The cathode layer includes a plurality of cathodes 35. In such an organic EL device, when a predetermined voltage is applied between the anode layer 34 and the cathode layer, holes from the anode layer 34 and electrons from the cathodes 35 are injected into the organic layer 33, wherein a hole is combined with an electron to generate light. By using the light radiated through the combination process of the holes and the electrons, i.e., one hole combining with one electron, it is possible to display desired images, e.g., alphanumeric characters and/or predetermined display patterns.
In such an organic EL device 31, each of such characters and patterns includes one or more luminous segments. The luminous segments forming the characters and patterns are organized into several groups and the luminous segments in each group are electrically connected to each other by a single cathode.
Referring to FIGS. 2A and 2B, there are shown a schematic cross sectional view setting forth formation of the cathodes 35 and a top view of a deposition mask 41 for use in forming the cathodes 35 of the organic EL device 31.
As shown in FIG. 2B, the deposition mask 41 is provided with a slit set 42 having three slits 42a, 42b, 42c corresponding to three groups of the luminous segments forming the characters and patterns. After depositing the anode layer 34 made of a transparent material, e.g., ITO (indium tin oxide) on the substrate 32 and then forming thereon the organic layer 33 made of an organic compound, the cathodes 35 are formed on the organic layer 33 by aligning the deposition mask 41 thereon and depositing, e.g., by evaporation, a conductive material therethrough, resulting in obtaining the cathodes 35, each having shape identical to the shape of corresponding one of the slits 42a, 42b, 42c of the deposition mask 41.
In such an organic EL device having the cathodes formed by using the mask, each of the cathodes is formed in an elongated slit shape. When forming the elongated slit-shaped cathodes by a mask deposition technique described above, there often occurs an electrical insulation failure due to bending or deformation of the mask.
To be more specific, when the widths of the slits of the mask are narrow, the thickness of the mask plate is required to be small. When the masking area is smaller than the depositing area (opening area of the mask, i.e., the area of the slits), the mask becomes less rigid or pliant. As a result, the mask can be readily deformed and it becomes difficult to handle the mask, thereby lowering the manufacturing efficiency and yield thereof. Further, the organic layer can be damaged by bending of the mask during the alignment of the mask with the substrate having thereon the anode layer and the organic layer deposited in sequence, thereby degrading the quality of display.
It is, therefore, an object of the present invention to provide an organic electroluminescent device and a manufacturing method thereof, wherein an electrode layer made of patterned electrodes is formed by using a deposition mask without causing an electrical insulation failure between the electrodes and degradation of the display quality. The deposition mask of the invention eliminates or reduces the bending and deformation problems of the prior art deposition mask, to thereby improve the manufacturing efficiency and yield thereof.
In accordance with one aspect of the present invention, there is provided an organic electroluminescent device comprising:
an insulating substrate;
a first electrode layer, a second electrode layer, and a number of conductive wiring pads formed on the insulating substrate, wherein at least one of the electrode layers is transparent and the second electrode layer includes a plurality of disjointed electrodes, the disjointed electrodes being grouped into a plural number of groups and at least one of the groups having at least two disjointed electrodes; and
an organic layer interposed between the first and the second electrode layers,
wherein the electrodes of each of said at least one of the groups are electrically connected to each other via one or more selected wiring pads.
In accordance with another aspect of the present invention, there is provided a method for manufacturing an organic electroluminescent device comprising the steps of:
forming a first electrode layer on an insulting substrate;
forming wiring pads made of a first conductive material;
forming an organic layer on the first electrode layer; and
forming a second electrode layer on the organic layer by depositing a second conductive material through a mask, wherein the second electrode layer includes a plurality of disjointed electrodes and the disjointed electrodes are grouped into a plural number of groups, at least one of the groups having at least two disjointed electrodes,
wherein at least one of the electrodes is transparent and said electrodes of each of said at least one of the groups are electrically connected to each other via one or more selected wiring pads.
In accordance with a further aspect of the present invention, there is provided a method for manufacturing an organic electroluminescent device comprising the steps of:
simultaneously forming a first electrode layer and wiring pads made of a first conductive material on a transparent substrate;
forming an insulation layer on the structure obtained by the simultaneously forming step in such a way that a selected portion of the first electrode layer and at least a portion of each wiring pad are exposed;
forming an organic layer on the exposed first electrode layer; and
forming a second electrode layer on the organic layer and the exposed portions of the wiring pads by depositing a second conductive material through a mask, wherein the second electrode layer includes at least one group of separated electrodes and the separated electrodes included in each group are electrically connected to each other via exposed portions of selected one or more wiring pads.